The present invention relates essentially to a power-assisted steering device for automotive vehicles, of the kind comprising a power-assisted steering valve provided with a rotor made rotationally fast with the steering shaft, with a stationary body forming a box or case, with a tubular sleeve positioned in the box or case in coaxial relationship about the rotor and made rotationally fast with a member for mechanically operating the steering mechanism and with a resilient rotary drive connecting device interposed between the steering shaft and the mechanical operating member, which comprises a bar or rod extending along the centreline axis of the valve and made rotationally fast at one end with said mechanical operating member.
In known power-assisted steering devices of this type, the bar or rod of the resilient connecting device is shaped as a torsion bar the end of which that is opposite to that secured to the mechanical operating member is connected through a cotter pin to the steering shaft, hence to the valve rotor. To vary the extent of power assistance of the steering valve, the flow rate or the pressure of the fluid flowing in the circuit of the valve is varied.
These measures to vary the extent or degree of power assistance however exhibit inconveniences. Thus, the decrease in the flow rate may result in some idleness or in a heaviness of the steering and in some softness between the steering wheel angle and the angle of the wheels. Consequently, the variation in the flow rate is limited and the variation in the powered assistance is restricted too. The variation in the degree or extent of assistance through variation in the pressure would meet with difficulties in varying the pressure in an accurate and stable manner in accordance with the speed and a softness between the angle of the steering wheel and the angle of the wheels may occur.